Much of the steel produced by mills is in the form of coiled steel sheet, but rarely does the sheet correspond in width to the multitude of products that are stamped or otherwise formed from it. Accordingly, the steel sheet is usually slit longitudinally to sizes suitable for the particular products. Indeed, special slitting machines are made for this purpose.
The typical slitting machine has circular blades or knives arranged in pairs on two powered shafts or arbors, there being one knife of each pair on one of the arbors and the second knife of the pair on the other arbor. The arbors are connected to a drive system for counter-rotation. During operation, sheet metal is moved between the arbors and cut into mults by the knives counter-rotating on the arbors. Actually each knife is nothing more than a hardened steel disk having flat end faces and a cylindrical peripheral face which intersects the end faces at relatively sharp cutting or shearing edges. The disks of each pair are positioned on their respective arbors, often with a slight overlap. Overlap or not, the knives of each pair are positioned close enough to each other to enable them to cut or shear the metal sheet as it passes between those knives. In other words, the metal sheet is drawn between the two knives of a pair the disk-like knives shear the sheet along the opposite cutting edges, thus producing a clean longitudinal cut in the sheet. Not only are the disk-like knives arranged in pairs, but the pairs of knives are also usually organized into left and right hand configurations to prevent the longitudinal segments of the slit sheet from acquiring a twist or spiral upon emerging from the slitting machine.
The size of the mults is determined by the spacing of the knives on the arbors. The knives, while being fixed firmly on their respective arbors during the operation of the machine, nevertheless may be removed for sharpening or may be repositioned so that the width of the segments slit may be varied. Setting the knives on the arbors of a slitting machine however is a tedious and time-consuming procedure, requiring a high degree of skill, for the knives must be located with considerable precision, not only to acquire the proper width for the cut, but to also maintain a clean high quality cut as well.
In one type of slitting machine, the knives are carried on hubs that slide over the arbor and are secured with set screws in the desired positions. To set the knives of a pair in the proper position, the location of the cut desired from the pair of knives is usually located by measuring with a tape measure from reference point on the machine. One of the knives is then moved over its arbor to the point located with the tape measure and the set screw of its hub is turned down to secure the knife. Once the knife is so positioned, an indicator gage should be brought against it while the arbor is turned slowly. With the indicator gage the knife is checked for wobble and usually adjustments must be made by loosening the set screws and tapping the knife lightly to eliminate the wobble. The same procedure is then repeated with the other knife of the pair, only its location is determined from the location of the previous knife, there usually being an axial gap on the order of 7 to 10 percent of the thickness of the metal sheet between the opposite cutting edges of the two knives. To change the size and number of mults produced from the sheet metal, the hubs must be released from the arbors and moved to new locations. New hubs would be added, or existing hubs removed, as dictated by changes in the number of mults to be cut in the sheet metal.
In another type of slitting machine, spacers separate the knives. These spacers are large enough and are machined with enough precision to minimize the wobble inherent with conventional arbors, but present complexities in the selection of spacers and shims to properly locate the knives. The selection of spacers and shims requires a considerable amount of skill. Furthermore, the spacers must be handled carefully, to avoid nicks that will skew the knives and create a wobble as they rotate.
To change the size and number of mults produced from the sheet metal, the spacers must be removed from the arbor and replaced with a new set of spacers adapted to the new cutting pattern.
In the past, such replacements and adjustments were generally performed by hand. This use of manual labor was expensive and slowed the process of conversion from one cutting job to the next. The task of replacement and adjustment was difficult physically, often requiring workers to lift the heavy hubs or spacers to uncomfortable heights. Furthermore, where spacers were used, it was necessary to maintain a sizable inventory of such spacers to provide flexibility in cutting different sizes and numbers of mults.
One prior attempt to solve such problems is disclosed in U.S. Pat. No. 4,887,502 directed to a machine for slitting metal. The machine includes upper and lower powered arbors and also upper and lower storage arbors which align respectively with the upper and lower powered arbors. Each powered arbor supports and turns several knives which are mounted on hubs along those arbors, and these knives when not needed may be moved, along with their hubs, onto the aligned storage arbors. Each knife is captured in a carriage which moves along one of the beams. The knives are positioned through a lead screw which drives a carriage having stops against which knives on the upper and lower arbors are manually moved and set in position through contact with the stops. The carriage may also be provided with fingers which actually capture the knives of a pair and move them to the correct position.
To eliminate the need to reconfigure a slitting machine for a particular slitting operation, a slitting line may include multiple slitters having different knife configurations that can be moved into and out of the line.
There remains a need in the art for slitting machines which can be automatically set up and adjusted, including the replacement or servicing of knives on the arbors, with minimal labor on the part of the operator or user.